A one-dimensional stochastic model of turbulence within and above plant canopies

The suitability of Kerstein's One-Dimensional Turbulence (ODT) model in the representation of atmospheric boundary layer (ABL) flows within and above plant canopies is investigated. The ODT model was adapted to represent a filtered version of flow and scalar fields, equipped with a Smagorinsky-like sub-grid scale model, a wall model, and a parameterization of the canopy effects on the flow. In the filtered ODT, the entire vertical extension of the ABL is modeled and the “resolved” vertical turbulent transport is represented by stochastic eddies that effectively mix fluid parcels across a path length, representing non-local turbulent fluxes that are a critical feature of the canopy roughness sublayer. Simulations for different canopies and stability conditions are performed and vertical profiles of turbulence and scalar statistics are compared with observational and large-eddy simulation data. This new filtered version of the ODT model yields grid-independent results. Model performance for plant canopies is consistent with previous results from ODT for all cases tested without any case-specific parameter adjustment, generating reasonable agreement in profiles of mean velocity, temperature and water vapor mixing ratio, as well as vertical fluxes of momentum and sensible and latent heat, despite the underestimation of all velocity variances. Non-local transport is intrinsic to the formulation of ODT, which represents a significant advantage compared to other reduced-model approaches employed for canopy flows.